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  Leetcode-146-LRU缓存机制
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      <h1 id="Leecode-146-LRU缓存机制"><a href="#Leecode-146-LRU缓存机制" class="headerlink" title="Leecode-146. LRU缓存机制"></a>Leecode-<a href="https://leetcode-cn.com/problems/lru-cache/" target="_blank" rel="noopener">146. LRU缓存机制</a></h1><h2 id="思路：递归-迭代"><a href="#思路：递归-迭代" class="headerlink" title="思路：递归/迭代"></a>思路：递归/迭代</h2><h2 id="题目描述"><a href="#题目描述" class="headerlink" title="题目描述"></a>题目描述</h2><p>运用你所掌握的数据结构，设计和实现一个  LRU (最近最少使用) 缓存机制。它应该支持以下操作： 获取数据 get 和 写入数据 put 。</p>
<ul>
<li>获取数据 get(key) - 如果关键字 (key) 存在于缓存中，则获取关键字的值（总是正数），否则返回 -1。</li>
<li>写入数据 put(key, value) - 如果关键字已经存在，则变更其数据值；如果关键字不存在，则插入该组「关键字/值」。当缓存容量达到上限时，它应该在写入新数据之前删除最久未使用的数据值，从而为新的数据值留出空间。</li>
</ul>
<h2 id="方案：-哈希链表"><a href="#方案：-哈希链表" class="headerlink" title="方案： 哈希链表"></a>方案： 哈希链表</h2><ul>
<li>LRU 算法实际上是让你设计数据结构：首先要接收一个 capacity 参数作为缓存的最大容量，然后实现两个 API，一个是 put(key, val) 方法存入键值对，另一个是 get(key) 方法获取 key 对应的 val，如果 key 不存在则返回 -1。</li>
<li>注意哦，get 和 put 方法必须都是 O(1) 的时间复杂度，我们举个具体例子来看看 LRU 算法怎么工作。</li>
</ul>
<a id="more"></a>

<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br></pre></td><td class="code"><pre><span class="line">&#x2F;* 缓存容量为 2 *&#x2F;</span><br><span class="line">LRUCache cache &#x3D; new LRUCache(2);</span><br><span class="line">&#x2F;&#x2F; 你可以把 cache 理解成一个队列</span><br><span class="line">&#x2F;&#x2F; 假设左边是队头，右边是队尾</span><br><span class="line">&#x2F;&#x2F; 最近使用的排在队头，久未使用的排在队尾</span><br><span class="line">&#x2F;&#x2F; 圆括号表示键值对 (key, val)</span><br><span class="line"></span><br><span class="line">cache.put(1, 1);</span><br><span class="line">&#x2F;&#x2F; cache &#x3D; [(1, 1)]</span><br><span class="line">cache.put(2, 2);</span><br><span class="line">&#x2F;&#x2F; cache &#x3D; [(2, 2), (1, 1)]</span><br><span class="line">cache.get(1);       &#x2F;&#x2F; 返回 1</span><br><span class="line">&#x2F;&#x2F; cache &#x3D; [(1, 1), (2, 2)]</span><br><span class="line">&#x2F;&#x2F; 解释：因为最近访问了键 1，所以提前至队头</span><br><span class="line">&#x2F;&#x2F; 返回键 1 对应的值 1</span><br><span class="line">cache.put(3, 3);</span><br><span class="line">&#x2F;&#x2F; cache &#x3D; [(3, 3), (1, 1)]</span><br><span class="line">&#x2F;&#x2F; 解释：缓存容量已满，需要删除内容空出位置</span><br><span class="line">&#x2F;&#x2F; 优先删除久未使用的数据，也就是队尾的数据</span><br><span class="line">&#x2F;&#x2F; 然后把新的数据插入队头</span><br><span class="line">cache.get(2);       &#x2F;&#x2F; 返回 -1 (未找到)</span><br><span class="line">&#x2F;&#x2F; cache &#x3D; [(3, 3), (1, 1)]</span><br><span class="line">&#x2F;&#x2F; 解释：cache 中不存在键为 2 的数据</span><br><span class="line">cache.put(1, 4);    </span><br><span class="line">&#x2F;&#x2F; cache &#x3D; [(1, 4), (3, 3)]</span><br><span class="line">&#x2F;&#x2F; 解释：键 1 已存在，把原始值 1 覆盖为 4</span><br><span class="line">&#x2F;&#x2F; 不要忘了也要将键值对提前到队头</span><br></pre></td></tr></table></figure>



<ul>
<li>分析上面的操作过程，要让 put 和 get 方法的时间复杂度为 O(1)，我们可以总结出 cache 这个数据结构必要的条件：查找快，插入快，删除快，有顺序之分。</li>
<li>因为显然 cache <strong>必须有顺序之分</strong>，以区分最近使用的和久未使用的数据；而且我们要在 cache 中查找键是否已存在；<strong>如果容量满了要删除最后一个数据；每次访问还要把数据插入到队头。</strong></li>
<li>那么，什么数据结构同时符合上述条件呢？<strong>哈希表查找快，但是数据无固定顺序</strong>；<strong>链表有顺序之分，插入删除快，但是查找慢。</strong>所以结合一下，形成一种新的数据结构：哈希链表。</li>
<li><strong>LRU 缓存算法的核心数据结构就是哈希链表</strong>，双向链表和哈希表的结合体。这个数据结构长这样：</li>
</ul>
<p><img src="http://zhuuu-bucket.oss-cn-beijing.aliyuncs.com/img/20200805-165923396.png" alt="mark"></p>
<p><strong>思想很简单，就是借助哈希表赋予了链表快速查找的特性嘛：可以快速查找某个 key 是否存在缓存（链表）中，同时可以快速删除、添加节点。回想刚才的例子，这种数据结构是不是完美解决了 LRU 缓存的需求？</strong></p>
<p>也许读者会问，为什么要是双向链表，单链表行不行？另外，既然哈希表中已经存了 key，为什么链表中还要存键值对呢，只存值不就行了？</p>
<p>想的时候都是问题，只有做的时候才有答案。这样设计的原因，必须等我们亲自实现 LRU 算法之后才能理解，所以我们开始看代码吧～</p>
<p><strong>代码实现</strong></p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br></pre></td><td class="code"><pre><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">LRUCache</span> <span class="keyword">extends</span> <span class="title">LinkedHashMap</span>&lt;<span class="title">Integer</span>, <span class="title">Integer</span>&gt;</span>&#123;</span><br><span class="line">    <span class="keyword">private</span> <span class="keyword">int</span> capacity;</span><br><span class="line">    </span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="title">LRUCache</span><span class="params">(<span class="keyword">int</span> capacity)</span> </span>&#123;</span><br><span class="line">        <span class="keyword">super</span>(capacity, <span class="number">0.75F</span>, <span class="keyword">true</span>);</span><br><span class="line">        <span class="keyword">this</span>.capacity = capacity;</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">int</span> <span class="title">get</span><span class="params">(<span class="keyword">int</span> key)</span> </span>&#123;</span><br><span class="line">        <span class="keyword">return</span> <span class="keyword">super</span>.getOrDefault(key, -<span class="number">1</span>);</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">    <span class="comment">// 这个可不写</span></span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">put</span><span class="params">(<span class="keyword">int</span> key, <span class="keyword">int</span> value)</span> </span>&#123;</span><br><span class="line">        <span class="keyword">super</span>.put(key, value);</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">    <span class="meta">@Override</span></span><br><span class="line">    <span class="function"><span class="keyword">protected</span> <span class="keyword">boolean</span> <span class="title">removeEldestEntry</span><span class="params">(Map.Entry&lt;Integer, Integer&gt; eldest)</span> </span>&#123;</span><br><span class="line">        <span class="keyword">return</span> size() &gt; capacity; </span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>







<p><strong>手动实现版本</strong></p>
<ol>
<li><strong>Node结构</strong></li>
</ol>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">Node</span> </span>&#123;</span><br><span class="line">    <span class="keyword">public</span> <span class="keyword">int</span> key, val;</span><br><span class="line">    <span class="keyword">public</span> Node next, prev;</span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="title">Node</span><span class="params">(<span class="keyword">int</span> k, <span class="keyword">int</span> v)</span> </span>&#123;</span><br><span class="line">        <span class="keyword">this</span>.key = k;</span><br><span class="line">        <span class="keyword">this</span>.val = v;</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>



<ol start="2">
<li><strong>双向链表</strong></li>
</ol>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br></pre></td><td class="code"><pre><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">DoubleList</span> </span>&#123;</span><br><span class="line">    <span class="keyword">private</span> Node head, tail; <span class="comment">// 头尾虚节点</span></span><br><span class="line">    <span class="keyword">private</span> <span class="keyword">int</span> size; <span class="comment">// 链表元素数</span></span><br><span class="line"></span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="title">DoubleList</span><span class="params">()</span> </span>&#123;</span><br><span class="line">        head = <span class="keyword">new</span> Node(<span class="number">0</span>, <span class="number">0</span>);</span><br><span class="line">        tail = <span class="keyword">new</span> Node(<span class="number">0</span>, <span class="number">0</span>);</span><br><span class="line">        head.next = tail;</span><br><span class="line">        tail.prev = head;</span><br><span class="line">        size = <span class="number">0</span>;</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">    <span class="comment">// 在链表头部添加节点 x</span></span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">addFirst</span><span class="params">(Node x)</span> </span>&#123;</span><br><span class="line">        x.next = head.next;</span><br><span class="line">        x.prev = head;</span><br><span class="line">        head.next.prev = x;</span><br><span class="line">        head.next = x;</span><br><span class="line">        size++;</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">    <span class="comment">// 删除链表中的 x 节点（x 一定存在）</span></span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">remove</span><span class="params">(Node x)</span> </span>&#123;</span><br><span class="line">        x.prev.next = x.next;</span><br><span class="line">        x.next.prev = x.prev;</span><br><span class="line">        size--;</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">    <span class="comment">// 删除链表中最后一个节点，并返回该节点</span></span><br><span class="line">    <span class="function"><span class="keyword">public</span> Node <span class="title">removeLast</span><span class="params">()</span> </span>&#123;</span><br><span class="line">        <span class="keyword">if</span> (tail.prev == head)</span><br><span class="line">            <span class="keyword">return</span> <span class="keyword">null</span>;</span><br><span class="line">        Node last = tail.prev;</span><br><span class="line">        remove(last);</span><br><span class="line">        <span class="keyword">return</span> last;</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">    <span class="comment">// 返回链表长度</span></span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">int</span> <span class="title">size</span><span class="params">()</span> </span>&#123; <span class="keyword">return</span> size; &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>



<ol start="3">
<li><strong>缓存实现</strong></li>
</ol>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br><span class="line">45</span><br><span class="line">46</span><br><span class="line">47</span><br><span class="line">48</span><br><span class="line">49</span><br><span class="line">50</span><br><span class="line">51</span><br><span class="line">52</span><br><span class="line">53</span><br><span class="line">54</span><br><span class="line">55</span><br><span class="line">56</span><br><span class="line">57</span><br><span class="line">58</span><br><span class="line">59</span><br><span class="line">60</span><br><span class="line">61</span><br><span class="line">62</span><br><span class="line">63</span><br><span class="line">64</span><br><span class="line">65</span><br><span class="line">66</span><br><span class="line">67</span><br><span class="line">68</span><br><span class="line">69</span><br><span class="line">70</span><br><span class="line">71</span><br><span class="line">72</span><br><span class="line">73</span><br><span class="line">74</span><br><span class="line">75</span><br><span class="line">76</span><br><span class="line">77</span><br><span class="line">78</span><br><span class="line">79</span><br><span class="line">80</span><br><span class="line">81</span><br><span class="line">82</span><br><span class="line">83</span><br><span class="line">84</span><br><span class="line">85</span><br><span class="line">86</span><br><span class="line">87</span><br><span class="line">88</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">import</span> java.util.HashMap;</span><br><span class="line"></span><br><span class="line"></span><br><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">LRUCache</span> </span>&#123;</span><br><span class="line"></span><br><span class="line">    <span class="comment">// key -&gt; Node(key, val)</span></span><br><span class="line">    <span class="keyword">private</span> HashMap&lt;Integer,Node&gt; map;</span><br><span class="line">    <span class="comment">// Node(k1, v1) &lt;-&gt; Node(k2, v2)...</span></span><br><span class="line">    <span class="keyword">private</span> DoubleList cache;</span><br><span class="line">    <span class="comment">// 最大容量</span></span><br><span class="line">    <span class="keyword">private</span> <span class="keyword">int</span> cap;</span><br><span class="line"></span><br><span class="line"></span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="title">LRUCache</span><span class="params">(<span class="keyword">int</span> capacity)</span> </span>&#123;</span><br><span class="line">        <span class="keyword">this</span>.cap = capacity;</span><br><span class="line">        map = <span class="keyword">new</span> HashMap&lt;&gt;();</span><br><span class="line">        cache = <span class="keyword">new</span> DoubleList();</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">int</span> <span class="title">get</span><span class="params">(<span class="keyword">int</span> key)</span> </span>&#123;</span><br><span class="line">        <span class="comment">// 如果不存在</span></span><br><span class="line">        <span class="keyword">if</span> (!map.containsKey(key))&#123;</span><br><span class="line">            <span class="keyword">return</span> -<span class="number">1</span>;</span><br><span class="line">        &#125;</span><br><span class="line"></span><br><span class="line">        <span class="keyword">int</span> val = map.get(key).val;</span><br><span class="line">        <span class="comment">// 利用 put 方法把该数据提前</span></span><br><span class="line">        put(key,val);</span><br><span class="line">        <span class="keyword">return</span> val;</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">put</span><span class="params">(<span class="keyword">int</span> key, <span class="keyword">int</span> value)</span> </span>&#123;</span><br><span class="line">        <span class="comment">// 先把新节点 x new出来</span></span><br><span class="line">        Node x = <span class="keyword">new</span> Node(key,value);</span><br><span class="line"></span><br><span class="line">        <span class="comment">// 如果之前key存在</span></span><br><span class="line">        <span class="keyword">if</span> (map.containsKey(key))&#123;</span><br><span class="line">            <span class="comment">// 删除旧的节点，新的插入到头部</span></span><br><span class="line">            cache.remove(map.get(key));</span><br><span class="line">            cache.addFirst(x);</span><br><span class="line"></span><br><span class="line">            <span class="comment">// 更新map对应的数据</span></span><br><span class="line">            map.put(key,x);</span><br><span class="line">        &#125;<span class="keyword">else</span> &#123;</span><br><span class="line">            <span class="comment">// 如果之前key不存在</span></span><br><span class="line">            <span class="keyword">if</span> (cap == cache.size())&#123;</span><br><span class="line">                <span class="comment">// 删除链表的最后一个数据</span></span><br><span class="line">                Node last = cache.removeLast();</span><br><span class="line">                map.remove(last.key);</span><br><span class="line">            &#125;</span><br><span class="line">            <span class="comment">// 直接添加到头部</span></span><br><span class="line">            cache.addFirst(x);</span><br><span class="line">            map.put(key,x);</span><br><span class="line">        &#125;</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line"></span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">void</span> <span class="title">main</span><span class="params">(String[] args)</span> </span>&#123;</span><br><span class="line">        LRUCache cache = <span class="keyword">new</span> LRUCache(<span class="number">2</span>);</span><br><span class="line">        cache.put(<span class="number">1</span>, <span class="number">1</span>);</span><br><span class="line">        cache.put(<span class="number">2</span>, <span class="number">2</span>);</span><br><span class="line">        System.out.println(cache.map.keySet());</span><br><span class="line"></span><br><span class="line">        <span class="keyword">int</span> res1 = cache.get(<span class="number">1</span>);</span><br><span class="line">        System.out.println(res1);</span><br><span class="line"></span><br><span class="line">        cache.put(<span class="number">3</span>, <span class="number">3</span>);</span><br><span class="line"></span><br><span class="line">        <span class="keyword">int</span> res2 = cache.get(<span class="number">2</span>);</span><br><span class="line">        System.out.println(res2);</span><br><span class="line"></span><br><span class="line">        <span class="keyword">int</span> res3 = cache.get(<span class="number">3</span>);</span><br><span class="line">        System.out.println(res3);</span><br><span class="line"></span><br><span class="line">        cache.put(<span class="number">4</span>, <span class="number">4</span>);</span><br><span class="line">        System.out.println(cache.map.keySet());</span><br><span class="line"></span><br><span class="line">        <span class="keyword">int</span> res4 = cache.get(<span class="number">1</span>);</span><br><span class="line">        System.out.println(res4);</span><br><span class="line"></span><br><span class="line">        <span class="keyword">int</span> res5 = cache.get(<span class="number">3</span>);</span><br><span class="line">        System.out.println(res5);</span><br><span class="line"></span><br><span class="line">        <span class="keyword">int</span> res6 = cache.get(<span class="number">4</span>);</span><br><span class="line">        System.out.println(res6);</span><br><span class="line"></span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>





<p><strong>补充一段伪代码逻辑</strong></p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">// key 映射到 Node(key, val)</span></span><br><span class="line">HashMap&lt;Integer, Node&gt; map;</span><br><span class="line"><span class="comment">// Node(k1, v1) &lt;-&gt; Node(k2, v2)...</span></span><br><span class="line">DoubleList cache;</span><br><span class="line"></span><br><span class="line"><span class="function"><span class="keyword">int</span> <span class="title">get</span><span class="params">(<span class="keyword">int</span> key)</span> </span>&#123;</span><br><span class="line">    <span class="keyword">if</span> (key 不存在) &#123;</span><br><span class="line">        <span class="keyword">return</span> -<span class="number">1</span>;</span><br><span class="line">    &#125; <span class="keyword">else</span> &#123;        </span><br><span class="line">        将数据 (key, val) 提到开头；</span><br><span class="line">        <span class="keyword">return</span> val;</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line"><span class="function"><span class="keyword">void</span> <span class="title">put</span><span class="params">(<span class="keyword">int</span> key, <span class="keyword">int</span> val)</span> </span>&#123;</span><br><span class="line">    Node x = <span class="keyword">new</span> Node(key, val);</span><br><span class="line">    <span class="keyword">if</span> (key 已存在) &#123;</span><br><span class="line">        把旧的数据删除；</span><br><span class="line">        将新节点 x 插入到开头；</span><br><span class="line">    &#125; <span class="keyword">else</span> &#123;</span><br><span class="line">        <span class="keyword">if</span> (cache 已满) &#123;</span><br><span class="line">            删除链表的最后一个数据腾位置；</span><br><span class="line">            删除 map 中映射到该数据的键；</span><br><span class="line">        &#125; </span><br><span class="line">        将新节点 x 插入到开头；</span><br><span class="line">        map 中新建 key 对新节点 x 的映射；</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>


      
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    contentSelector: '.article-entry',
    headingSelector: 'h1, h2, h3, h4, h5, h6',
    hasInnerContainers: true,
    scrollSmooth: true,
    scrollContainer:'main',
    positionFixedSelector: '.tocbot',
    positionFixedClass: 'is-position-fixed',
    fixedSidebarOffset: 'auto',
    onClick: (e) => {
      $('.toc-link').removeClass('is-active-link');
      $(`a[href=${e.target.hash}]`).addClass('is-active-link');
      $(e.target.hash).scrollIntoView();
      return false;
    }
  });
</script>


<script>
  var ayerConfig = {
    mathjax: true
  }
</script>


<script src="/js/ayer.js"></script>


<script src="https://cdn.jsdelivr.net/npm/jquery-modal@0.9.2/jquery.modal.min.js"></script>
<link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/jquery-modal@0.9.2/jquery.modal.min.css">


<!-- Root element of PhotoSwipe. Must have class pswp. -->
<div class="pswp" tabindex="-1" role="dialog" aria-hidden="true">

    <!-- Background of PhotoSwipe. 
         It's a separate element as animating opacity is faster than rgba(). -->
    <div class="pswp__bg"></div>

    <!-- Slides wrapper with overflow:hidden. -->
    <div class="pswp__scroll-wrap">

        <!-- Container that holds slides. 
            PhotoSwipe keeps only 3 of them in the DOM to save memory.
            Don't modify these 3 pswp__item elements, data is added later on. -->
        <div class="pswp__container">
            <div class="pswp__item"></div>
            <div class="pswp__item"></div>
            <div class="pswp__item"></div>
        </div>

        <!-- Default (PhotoSwipeUI_Default) interface on top of sliding area. Can be changed. -->
        <div class="pswp__ui pswp__ui--hidden">

            <div class="pswp__top-bar">

                <!--  Controls are self-explanatory. Order can be changed. -->

                <div class="pswp__counter"></div>

                <button class="pswp__button pswp__button--close" title="Close (Esc)"></button>

                <button class="pswp__button pswp__button--share" style="display:none" title="Share"></button>

                <button class="pswp__button pswp__button--fs" title="Toggle fullscreen"></button>

                <button class="pswp__button pswp__button--zoom" title="Zoom in/out"></button>

                <!-- Preloader demo http://codepen.io/dimsemenov/pen/yyBWoR -->
                <!-- element will get class pswp__preloader--active when preloader is running -->
                <div class="pswp__preloader">
                    <div class="pswp__preloader__icn">
                        <div class="pswp__preloader__cut">
                            <div class="pswp__preloader__donut"></div>
                        </div>
                    </div>
                </div>
            </div>

            <div class="pswp__share-modal pswp__share-modal--hidden pswp__single-tap">
                <div class="pswp__share-tooltip"></div>
            </div>

            <button class="pswp__button pswp__button--arrow--left" title="Previous (arrow left)">
            </button>

            <button class="pswp__button pswp__button--arrow--right" title="Next (arrow right)">
            </button>

            <div class="pswp__caption">
                <div class="pswp__caption__center"></div>
            </div>

        </div>

    </div>

</div>

<link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/photoswipe@4.1.3/dist/photoswipe.min.css">
<link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/photoswipe@4.1.3/dist/default-skin/default-skin.css">
<script src="https://cdn.jsdelivr.net/npm/photoswipe@4.1.3/dist/photoswipe.min.js"></script>
<script src="https://cdn.jsdelivr.net/npm/photoswipe@4.1.3/dist/photoswipe-ui-default.min.js"></script>

<script>
    function viewer_init() {
        let pswpElement = document.querySelectorAll('.pswp')[0];
        let $imgArr = document.querySelectorAll(('.article-entry img:not(.reward-img)'))

        $imgArr.forEach(($em, i) => {
            $em.onclick = () => {
                // slider展开状态
                // todo: 这样不好，后面改成状态
                if (document.querySelector('.left-col.show')) return
                let items = []
                $imgArr.forEach(($em2, i2) => {
                    let img = $em2.getAttribute('data-idx', i2)
                    let src = $em2.getAttribute('data-target') || $em2.getAttribute('src')
                    let title = $em2.getAttribute('alt')
                    // 获得原图尺寸
                    const image = new Image()
                    image.src = src
                    items.push({
                        src: src,
                        w: image.width || $em2.width,
                        h: image.height || $em2.height,
                        title: title
                    })
                })
                var gallery = new PhotoSwipe(pswpElement, PhotoSwipeUI_Default, items, {
                    index: parseInt(i)
                });
                gallery.init()
            }
        })
    }
    viewer_init()
</script>



<script type="text/x-mathjax-config">
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  MathJax.Hub.Queue(function() {
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